1. Field of the Invention
This invention relates to a multiflow turbojet engine secondary flow regulating device.
2. Summary of the Prior Art
In multiflow turbojet engines with a re-heating duct, the secondary flow of cold air must be controllable in order to provide satisfactory operation of the re-heat over a large range of sub-sonic or supersonic conditions of flight. The relative speed of the secondary flow must be controlled at its junction with the primary flow so that the degree of dilution will be optimized. Such control can be effected by regulating the secondary flow.
French Patent Specification No. 2 316 443 describes a device for varying the degree of dilution constituted by a diaphragm placed in the secondary duct and capable of regulating secondary flow by a reduction in the free section of the duct. The device comprises a number of consecutive peripheral vanes. Each of these vanes occupies a segment of the circumference and is movable in a radial plane of the engine. The vanes are pivoted at their ends on two fixed pivots parallel to the axis of the engine. The other end is actuated radially by the piston rod of an actuator. The actuator acts at the adjacent ends of two consecutive vanes whilst the other ends of the vanes engage against one of the ends of the others of the consecutive vanes. The variation in the section of the duct results in the formation of a star shaped configuration by projection into the duct of the ends controlled by the actuators.
In the inactive position, the device reduces the section of the flow passage and thus requires overdimensioning of the diameter of the secondary casing; moveover, the actuators, being disposed on the outer casing, increase the overall cross-section of the engine as a whole.
U.S. Pat. No. 3,344,606 describes a device for bleeding air at one stage of the compressor in order to supply the re-heating duct. The casing of the compressor concerned comprises openings delivering into an annular collector connected by passages to another collector surrounding the re-heat chamber. Each opening is provided with a vane which pivots at one of its ends about an axis tangential to the casing, and is disposed in a radial plane. The opening or the closure of the vanes is controlled by an actuator acting on an annulus capable of being displaced axially on inclined planes of the vanes.
The turbo jet engine described is not of the multiflow type and does not include a secondary annular duct surrounding the primary duct. Thus, neither the problem of a reduction in the free section of the duct when the device is inactive, nor an increase in the overall cross-section of the engine arises.
The bleeding of air from the compressor does not pose the same aerodynamic problems as the modification of the discharge into the permanent flow of air in an annular duct.